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Q. I run an oxidation ditch with extended aeration with 4 secondary clarifiers. I am having problems with solids carryover to the wiers, Our daily flows are minimal about 1500m3/day, split between 2 clarifiers in operation. The volume of these are 620m3 each standard rectangular design. Hydraulic flows are so low could this cause the problem? Solids in each clarifier is low about 200kg of mass per. Is there anything you can recommend to stop the carry over?

A. I would need to know more specifics about your operation. What kind of waste water are you treating, or in other words, what is in it? What is inlet BOD, COD, O&G, and are there any heavy metals? Is it metal finishing waste water, food industry, or sanitary waste water....or a mix, or something else? What chemicals and concentrations are in the waste water, like high sugar, grease, nitrogen?

What is your MLSS concentration in the oxidation ditch? Are you recycling solids from the clarifiers back to the oxidation ditch and if so what is the rate? Also what is your DO (disolved oxygen) concentration in the oxidation ditch? It needs to be controlled at about 2.0 mg/l of O2!